1. Field of the Invention
The present invention relates to ophthalmic lenses, and more particularly to soft contact lenses comprising one or more high modulus of elasticity zones in the peripheral region to stiffen the contact lenses for improved handling and a reduction in the tendency of the contact lens to fold.
2. Discussion of the Related Art
Myopia or nearsightedness is an optical or refractive defect of the eye wherein rays of light from an image focus to a point before they reach the retina. Myopia generally occurs because the eyeball or globe is too long or the shape or contour of the cornea is too steep. A minus powered spherical lens may be utilized to correct myopia. Hyperopia or farsightedness is an optical or refractive defect of the eye wherein rays of light from an image focus to a point after they reach or behind the retina. Hyperopia generally occurs because the eyeball or globe is too short or the shape or contour of the cornea is too flat. A plus powered spherical lens may be utilized to correct hyperopia. Astigmatism is an optical or refractive defect in which an individual's vision is blurred due to the inability of the eye to focus a point object into a focused image on the retina. Unlike myopia and/or hyperopia, astigmatism is unrelated to globe size or corneal steepness, but rather it is caused by a non-rotationally symmetric cornea or from the misalignment or positioning of the crystalline lens. The vast majority of astigmatism occurs due to non-rotationally symmetric corneal curvature. A perfect cornea is rotationally symmetric whereas in most individuals with astigmatism, the cornea is not rotationally symmetric. In other words, the cornea is actually more curved or steeper in one direction than another, thereby causing an image to be stretched out rather than focused to a point. A cylindrical lens or toric contact lens, rather than a spherical lens may be utilized to resolve astigmatism.
Typically, for astigmatic vision correction, mechanical features are designed into the periphery of the contact lens to achieve rotational stability on eye for the required vision correction. These mechanical features incorporate varying thicknesses around the lens periphery which may lead to the contact lenses having a propensity to fold in the package or during lens handling. In addition to folding, the contact lenses may not handle as well as contact lenses with uniform thickness.
Soft contact lenses are typically more comfortable to wear than rigid gas permeable hard contact lenses and this is due to the materials from which the contact lenses are fabricated; namely, silicone hydrogels. These materials have a low modulus of elasticity which makes them less stiff or rigid, thereby making the contact lenses more difficult to handle and prone to folding as is the case for contact lenses for astigmatic correction as explained above.
Accordingly, it would be advantageous to design contact lenses, that are made from silicone hydrogels, which may or may not comprise astigmatic correction, that have increased stiffness in the peripheral zones for improved handling and a reduction in the propensity of the lens to fold without sacrificing comfort.